Numerous voltage regulator circuits exist in the prior art.
A circuit of this type is disclosed in GB Patent No. 2 298 939, and is shown in FIG. 1A of the present description. This circuit includes a control transistor Q1 connected in series between an input terminal I and an output terminal O, and an output voltage detector D formed of two resistors Ra and Rb connected in series between output terminal O and the circuit's earth.
A voltage corresponding to the output voltage detected by detector D is compared to a reference voltage E3 by an operational amplifier AO, and the output voltage thereof is applied to the base terminal of a transistor Q2. Thus a base current of control transistor Q1 can be controlled by the output voltage of operational amplifier AO, via transistor Q2, so that the impedance of control transistor Q1 is controlled so as to provide a predetermined voltage at output terminal O.
One problem encountered during the operation of such a circuit lies in the unintentional appearance of phenomena known as &lt;&lt;latch-up&gt;&gt;which occur in an electronic component of the circuit, following external disturbances such as the supply of an electric voltage, an electric current or radiation.
&lt;&lt;Latch-up&gt;&gt;is commonly used to designate any phenomenon occurring in an integrated circuit following external disturbances such as the supply of an electric voltage, an electric current or radiation.
Numerous devices exist in the prior art for detecting &lt;&lt;latch-up&gt;&gt;in a substrate and, in particular, devices analysing a current capable of being disturbed by said phenomenon.
A device of this type is disclosed in Japanese Patent Application No. 5 326 825 in the name of FUNAI ELECTRIC CO LTD, and is shown in FIG. 1B of the present description. This device includes an integrated circuit IC1 at a first terminal of which is provided a supply voltage Vdd, via a bipolar transistor T1, and at the second terminal of which is connected a resonant circuit formed of a resistor R3 and a capacitor C3. A detection integrated circuit IC2 includes an earth terminal, a first terminal at which is provided supply voltage Vdd, and a second terminal connected to said resonant circuit as well as to the base terminal of a bipolar transistor T2 via a resistor R2. The base terminal of transistor T1 is connected to the collector terminal of transistor T2 via a resistor R1, and the emitter terminal of transistor T2 is earthed.
In the device described hereinbefore in relation to FIG. 1B, if latch-up occurs, a significant drop in supply voltage Vdd is detected by integrated circuit IC2. In this case, transistors T1 and T2 are blocked, and the voltage supplying integrated circuit IC1 is interrupted, which initialises the circuit. Subsequently, integrated circuit IC1 again operates normally.
However, these devices have complex structures and require a large number of electronic components to perform the detection and regulator functions.